1. Field of the Invention
The present invention is related to a method of managing E-UTRA function of user equipment and related communication system, and more particularly, to a method of deactivating and reactivating E-UTRA function according to mobility information of user equipment and related communication system.
2. Description of the Prior Art
The 3rd Generation Partnership Project (3GPP) has developed a 3rd Generation (3G) network system capable of providing high frequency spectrum utilization, universal coverage, and high-speed/quality multimedia data transmission. Examples of 3G network systems include the universal mobile telecommunications system (UMTS) and the global system for mobile communications edge radio access network (GERAN). In the UMTS, a radio access network known as a universal terrestrial radio access network (UTRAN) includes multiple base stations, commonly known as Node-Bs (NBs), for communicating with multiple user equipment (UE). Furthermore, a 4th Generation (4G) network system, also known as long-term evolution (LTE) system, is now being developed by the 3GPP in order to further improve performance of the UMTS to satisfy users' increasing needs. The LTE system includes a new radio interface and radio network architecture which provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved UTRAN (E-UTRAN) includes multiple evolved NBs (eNBs) for communicating with multiple UEs and a core network which includes a mobility management entity (MME), a serving gateway and other devices for NAS (Non Access Stratum) control.
When the E-UTRA function is activated, the user equipment can perform corresponding handover or cell reselection operations in order to switch from the UTRAN/GERAN to the E-UTRAN. According to a 3GPP specification TS 24.301, after deactivating the E-UTRA function, the user equipment is allowed to reactivate the E-UTRA function only after a predetermined waiting period has elapsed. If the length of the waiting period is too long, the user equipment may not be able to use 4G service for a long time, thereby influencing user experience. If the length of the waiting period is too short, the user equipment may repeatedly attempt to connect to a 4G network which has previously rejects the register request of the user equipment, thereby wasting time and power.